NXV

• Extension: nxv
• Samples: [1] (see note)

NXV is a container format used by the 2006 MP4 Player Watch manufactured by "Shenzhen Adragon Digitek" (China). The wrist watch is reported to support MP4, WMV and WMA, however this is achieved by first converting the files to the NXV format.

Container Format

The format consists of a sequence of 512-bytes packets.

Header packet:

 bytes  0-11   ASCIIZ  magic ("NXV File")
 bytes 12-19   ASCIIZ  version ("1.0.0", "3.0.1" or "3.0.2")
 byte     20   width (pixels)
 byte     21   height (pixels)
 byte  22-511  unknown - rand byte? (at least the first few bytes are required for video playback)

The a/v sequence commences at byte 512 with an audio packet:

 uint curSequence = 0
 while !eof
   u8[500]        audio payload
   u8[4]          unknown
   be32           sequence number
   le16           length (bytes)
   le16           unknown (pixels == bytes/2?)
   if (sequence == curSequence)
     curSequence += 1
     u8[length]     video payload

Audio Payload

The audio payload is an MP3 stream, including RIFF WAVE headers.

Video Payload

Raw video - be16 in 565 RGB format. If the version is "1.0.0", the video is at full-resolution. If the version is "3.0.1", the video is at quarter-resolution; that is, the video data is 1/4 of the size indicated and is scaled in each direction by two on playback. Version "3.0.2" seems to indicate a different format - likely sixteenth-resolution.

Notes

• Supported video resolutions are: 96x64, 96x80, 96x96, 128x96, 128x128, 160x128, 176x128. Despite the reduction in video resolution, the resulting NXV file size exceeds that of the input video file.
• Intermediate files are used by the NxvConverter program to store the audio and video payloads (filename.mp3 and filename.tmp) prior to muxing to the NXV file.
• All NXV files examined so far have one frame per video packet and the packets appear at regular intervals. Low and Mid quality have one frame per four audio packets; High quality has one frame for every two audio packets.
• The content of the sequence and length values in an audio packet not followed by a video packet is unknown - probably nothing.
• Example file is an encoding of public domain footage from Internet Archive: Moving Image Archive

External Links

• China Manufacturer of MP4 Player watch, An Long / "Adragon"
• Chinavasion - China wholesaler of MP4 Player watch
• Brando MP4 Watch Product Page
• Related doom9 thread including NXV software download
• Vendor website
• UNIX conversion utilities for non Windows users